Reservoir-type fuel injection system

ABSTRACT

In a reservoir-type fuel injection system, fuel can be supplied under pressure by a charge pump to two separate pressure reservoirs and the pressure reservoirs communicates via separate valve assemblies with injection nozzles via lines. By means of the separate reservoirs, overlapping of pre-injection and main injection events in different cylinders can be avoided.

The invention is based on a reservoir-type fuel injection system asdefined hereinafter.

In reservoir-type fuel injection systems of this kind, fuel is placed ina pressure reservoir under pressure by a charge pump that pumpscontinuously; a check valve is provided between the charge pump and thepressure reservoir to prevent fuel from being forced back into the pumpunder pressure in the intake stroke of the pump. Consequently,reservoir-type fuel injection systems require control devices thatmonitor the quantity and timing of the further supply of the fuel underpressure to the injection nozzle; rotating distributor shafts and/orvalve assemblies, particularly magnet valves are used for this purpose,for example. In typical reservoir-type fuel injection systems of thetype referred to the outset above, there is no separate regulation ofthe charge pump, and provision is made merely that the charge pump pumpan adequate quantity of fuel to the reservoir, which makes it impossibleto completely evacuate the reservoir, particularly at high rpm.

In reservoir-type fuel injection systems, injection can be done directlyinto the engine combustion chamber during both the intake stroke and thecompression stroke of an Otto engine. To improve emissions, it hasbecome known to divide the injection quantity into portions, inparticular a pre-injection quantity and a main injection quantity.Particularly in multi-cylinder engines, this can result in an overlap indrawing fuel from such a reservoir, and overlapping of pre-injection andmain injection events in various cylinders can occur. Such overlappingof injection events can consequently lead to problems in exact meteringof the injection quantities, and it is not readily possible to insuredefined injection quantities for various injection events.

From Japanese Patent Document A 57/212362, a reservoir-type fuelinjection system is known. In the known system, however, the tworeservoirs, one of which serves to store the fuel injection quantity forthe pre-injection and the other to store the fuel injection quantity fora main injection, communicate parallel to one another with the pump workchamber of the high-pressure pump, each via an interposed check valve.This arrangement has the disadvantage that upon filling of thereservoir, the quantity of fuel pumped per pump piston stroke by thehigh-pressure pump, which is embodied as a piston pump, is divided intothe two reservoirs, but there is no assurance as to which quantity offuel pumped by the high-pressure pump reaches which reservoir. Fillingof the various reservoirs depends on various parameters, such as theflow resistance, the opening pressure of the check valves, and thereservoir spring. The result, especially if, as is typical, thepre-injection quantity is kept very small, is a relatively major errorin the pre-injection metering quantity.

The embodiment of the reservoir-type fuel injection system according tothe invention, contrarily, has the advantage that by the strokelimitation of the movable wall such as a piston of the first reservoir,a defined fuel quantity can be pre-stored, and can in particularadvantageously be used for a pre-injection. For this kind of injection,the reservoir piston is always located in a defined outset positionbefore the metering of the applicable fuel injection quantity from thisreservoir is controlled. The stroke limitation assures that thefollowing reservoir will be reliably filled, and its movable wall willbe moved up to a position defined by opening the overflow opening. Atthe instant of metering a defined outset position of the movable wallthus exists, which increases the accuracy of injection and fuelmetering.

The embodiment of the reservoir-type fuel injection system according tothe invention further has the advantage that overlapping of injectionevents, particularly when the injection event is divided into apre-injection and a main injection event, can be avoided, and that itcan simultaneously be assured that for both the pre-injection and themain injection, not only the predefined quantity but also a predefinedpressure can be adhered to.

By means of the provisions recited herein, advantageous furtherdevelopments of and improvements to the reservoir-type fuel injectionsystem disclosed are possible.

A particularly simple structural embodiment can be attained by providingthat the separate reservoirs are coaxially arranged and have one commoncompression spring for both reservoir pistons. In this kind ofembodiment, it is also readily possible to make different pressurelevels available for the pre-injection and main injection; for thispurpose, the embodiment can be simply such that the pistons of thereservoirs have different cross-sectional areas.

Particularly in conjunction with multi-cylinder engines and acorrespondingly high number of switching events in the valves fordividing the injection into the pre-injection and main injection, it isespecially advantageous for the embodiment to be such that in additionto the magnet valves, a distributor valve, in particular a rotatingshaft with control bores or grooves, is incorporated into the line tothe injection nozzles; this kind of embodiment is known per se inconjunction with conventional reservoir-type fuel injection systems.

The invention will be described below in further detail in terms ofexemplary embodiments schematically shown in the drawing. Shown in thedrawing are FIG. 1, a schematic illustration of a first embodiment of areservoir-type fuel injection system according to the invention, andFIG. 2, a modified embodiment of a reservoir for use in a reservoir-typefuel injection system according to the invention.

In the reservoir-type fuel injection system of FIG. 1, a charge pump 1pumps fuel from a tank 2 via one way check valves 3, 4 through a commonfuel pressure line 5 into two pressure reservoirs 6 and 7; the movablewalls or pistons 8, 9 of the reservoirs are each acted upon by springs10 and 11. The reservoir 6, used for a pre-injection, has a stop 12 thatlimits the reservoir volume of the first reservoir 6. The reservoir 7used for a main injection has an overflow opening 13, so that if themaximum fill volume or maximum fill pressure of the reservoir 7 isexceeded, the overflow opening 13 is opened, and fuel can flow out underpressure into the tank or return line, again schematically representedby the numeral 2.

The two pressure reservoirs 6 and 7 communicate with injection nozzles,not shown in detail via pressure lines 14 and 15 and magnet valves 16and 17 disposed in those lines and via a distributor formed as arotationally driven rotary slide valve, 18 incorporated into thepressure lines downstream of the magnet valves 16, 17, depending on therotary position of the distributor valve 18; a feed line to an injectionnozzle of this kind is indicated in FIG. 1 by reference numeral 19. Inthe position of magnet valves 16 and 17 shown in FIG. 1, no drawing offuel from the pressure reservoirs takes place. Upon a switchover of themagnet valve 16, in the rotary position of the distributor valve 18shown, a pre-injection in a nozzle can be performed via the line 19. Asa result, after a corresponding rotation of the distributor valve 18,which is generally coupled to the camshaft, a main injection can also beperformed in the same injection nozzle, given appropriate switching ofthe magnet valve 17 in the pressure line 15.

As a result of the provision of two separate pressure reservoirs 6 and 7for a pre-injection and a main injection, a pre-injection and a maininjection can also be performed simultaneously in two differentcylinders, without thereby causing mutual influence of the variousinjection events on one another. Since the pre-injection quantitygenerally amounts to 10 to 20% of the main injection quantity, theembodiment shown in FIG. 1 assures that the piston 8 of the pressurereservoir 6 is always located on the defined stop. Mutual influence ofthe two pressure reservoirs 6 and 7 on one another is prevented by thecheck valve 4. By suitable dimensioning of the piston cross sections andcompression springs 10 and 11, different pressure levels can also bemaintained in the two pressure reservoirs.

It is assumed that the charge pump 1 furnishes a largely pulsation-freefeed flow, and that an adequate quantity of fuel is pumped into each ofthe reservoirs 6 and 7, so that even at maximum rpm, evacuation of thereservoirs 6 and 7 is prevented in any case. Besides the overflowopening 13 for limiting the maximum reservoir volume, a regulatingdevice, not shown in further detail, for a load-depending pumping by thecharge pump may be provided.

In the position of the magnet valves 16 and 17 shown in FIG. 1, a reliefof the pressure line 19 to the return line or to the tank 2 takes placevia check valves 20.

In the embodiment shown in FIG. 2, the charge pump 1 pumps via checkvalves 3 and 4 into a reservoir 21, in which two reservoir pistons 22and 23 are acted upon by a common compression spring 24. Thus bothreservoir pistons for the two separate pressure reservoirs for thepre-injection and the main injection are disposed coaxially to oneanother in a common housing; the reservoir piston 22 limits thereservoir space for the pre-injection and communicates with the pressureline 14, while the reservoir piston 23 limits the reservoir space forthe main injection and communicates with the pressure line 15. Thereservoir piston 22 can again be moved toward a stop 25, while thereservoir piston 23 cooperates with an overflow opening 26, which if themaximum reservoir volume is exceeded opens an outflow cross section inthe tank 2. As in the embodiment of FIG. 1, magnet valves 16 and 17,respectively and/or a distributor valve 18 to pressure lines 19 toinjection nozzles are again disposed in the lines 14 and 15. Bydimensioning the cross section and the reservoir pistons 22 and 23differently, it is assured that the pre-injection piston when acted uponwith pressurized fuel will rest on the stop 25 whenever no injection isbeing performed. Any possible influence on the injection events via thecoupling of the reservoir pistons 22 and 23 via the common compressionspring 24 can be ignored, given suitable spring dimensioning with a lowspring constant.

We claim:
 1. A reservoir-type fuel injection system having ahigh-pressure pump, which can be made to communicate with a firstreservoir (6) and a second reservoir (7), each reservoir is providedwith a wall (8, 9; 22, 23) that is movable relative to a restoring force(10, 11; 24) in each said reservoir, wherein the first reservoir (6) canbe decoupled from the high-pressure pump (1) by a first one-way checkvalve (3) and the second reservoir (7) can be decoupled from this saidhigh-pressure pump by a second one-way check valve (4), and wherein thefirst reservoir and the second reservoir can be made to communicate witha common injection nozzle via a first line (14) and a first, controlledvalve (16) that communicates directly with said first reservoir and asecond line (15) and a controlled valve (17) that communicates with saidsecond reservoir, said second reservoir (7; 21, 23) is also connected toan outlet side of the first reservoir (6; 21, 22) via the second checkvalve (4); and the first reservoir (6; 21, 22) has a stroke limitingstop (12; 25) for said movable wall (8; 22) therein and said secondreservoir (7; 21, 23) has an overflow opening (13; 26) controlled bysaid movable wall (9; 23) therein.
 2. A reservoir-type fuel injectionsystem as defined by claim 1, in which said first and second reservoirs(21) are coaxially disposed and have one common compression spring (24)for both reservoirs (22, 23).
 3. A reservoir-type fuel injection systemas defined by claim 1, in which said movable walls (8, 9, 22, 23) ofsaid first and second reservoirs (6, 7, 21) have differentcross-sectional areas.
 4. A reservoir-type fuel injection system asdefined by claim 2, in which said movable walls (8, 9, 22, 23) of saidfirst and second reservoirs (6, 7, 21) have different cross-sectionalareas.
 5. A reservoir-type fuel injection system as defined by claim 1,in which the controlled valves (16, 17) are magnet valves, the outletsof said valves can be made to communicate with the injection nozzles viaa distributor valve 18 in particular via a rotationally driven rotaryslide valve.
 6. A reservoir-type fuel injection system as defined byclaim 2, in which the controlled valves (16, 17) are magnet valves, theoutlets of said valves can be made to communicate with the injectionnozzles via a distributor valve 18 in particular via a rotationallydriven rotary slide valve.
 7. A reservoir-type fuel injection system asdefined by claim 3, in which the controlled valves (16, 17) are magnetvalves, the outlets of said valves can be made to communicate with theinjection nozzles via a distributor valve 18 in particular via arotationally driven rotary slide valve.
 8. A reservoir-type fuelinjection system as defined by claim 4, in which the controlled valves(16, 17) are magnet valves, the outlets of said valves can be made tocommunicate with the injection nozzles via a distributor valve 18 inparticular via a rotationally driven rotary slide valve.
 9. Areservoir-type fuel injection system as defined by claim 1, in which themovable wall (8, 9, 22, 23) of the first and second reservoirs (6, 7,21) have different cross-sectional areas.
 10. A reservoir-type fuelinjection system as defined by claim 2, in which the movable wall (8, 9,22, 23) of the first and second reservoirs (6, 7, 21) have differentcross-sectional areas.
 11. A reservoir-type fuel injection system asdefined by claim 3, in which the movable wall (8, 9, 22, 23) of thefirst and second reservoirs (6, 7, 21) have different cross-sectionalareas.
 12. A reservoir-type fuel injection system as defined by claim 4,in which the movable wall (8, 9, 22, 23) of the first and secondreservoirs (6, 7, 21) have different cross-sectional areas.
 13. Areservoir-type fuel injection system as defined by claim 1, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 14. Areservoir-type fuel injection system as defined by claim 2, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 15. Areservoir-type fuel injection system as defined by claim 3, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 16. Areservoir-type fuel injection system as defined by claim 4, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 17. Areservoir-type fuel injection system as defined by claim 9, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 18. Areservoir-type fuel injection system as defined by claim 10, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 19. Areservoir-type fuel injection system as defined by claim 11, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.
 20. Areservoir-type fuel injection system as defined by claim 12, whichincludes a rotating shaft distributor valve (18) with control boresincorporated into the line (14, 15) to the injection nozzles.